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It seems you are likely to lose a lot of intensity due to your
non-columnated light source.  With lasers, it doesn't matter how far you
are from the light source-it's the same intensity because the beam
divergence is minimal.  With arc lamps, energy density drops by radius
squared (surface area of a sphere).  Imagine the light path straightened
out - arc lamp to objective.  Measure the power that gets through an
aperature the diameter of your objective lens located that distance from
the lamp.  A 4mm dia objective 60cm from arc =.125 sqr cm/45,239 sqr cm
surface of sphere= 2.8x 10-6 efficiency of light getting from lamp to lens
assuming no losses other than geometry.

You can reduce this by placing a short focal length converging lens exactly
one focal length away from the arc.  This will capture a much larger
fraction of the light.  ( calculate area lens/area of sphere around lamp to
get max theoretical efficiency).



Chris Hunt
USDA Forest Products Laboratory
1 Gifford Pinchot Dr.
Madison, WI  53726
(608) 231-9521
Fax (608) 231-9521
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                      Matt Conklin
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                      Sent by: Confocal            Subject: UV uncaging questions
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                      04/23/2003 01:47 PM
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Dear confocalists,
         We are interested in using the scanhead of a BioRad MRC-600
confocal to direct UV uncaging of calcium (using NP-EGTA and fluo-4).
The idea being that we can uncage smaller areas using the electronic
zoom feature of  the confocal than if we used pinhole apertures along
the vertical illuminator lightpath. Because we are only interested in
getting the UV light to the cell to uncage, we are hoping to avoid
many of the problems/artifacts associated with emitted UV
fluorescence. However we are still concerned about a couple things.
First, we aren't using a UV laser, we are using a mercury arc lamp
(i.e. non-collimated light), is this a problem? Second, do
galvonometer mirrors reflect UV light? Our objective lens does
transmit UV light. The laser light is not fiber optically coupled to
the scanhead, and the UV light is directed into the scanhead through
the same opening the laser uses.
        Some advice as to the feasibility of this experiment would be
greatly appreciated, are we missing something obvious?


Matt



--
Matthew W. Conklin, Ph.D.
University of California-San Diego
Section of  Neurobiology
Rm. 3220 Pacific Hall
La Jolla, CA 92093-0357
(858)534-2456 (lab)
(858)581-6278 (home)